فصلنامه نانو مواد
پیاپی 9 (بهار 1390)

In the present work, TiO2/HAp nano-porous composite layers have been made by micro arc oxidation process in the electrolyte containing calcium acetate salts and β-glycerol phosphate with different concentrations and in various periods. Then the effects of these two variable parameters on phase structure, chemical composition, microstructures, and surface roughness of layers have been investigated. Studying the layers composition based on XRD and XPS techniques showed that they contain HAp phases, anatase, calcium titanate and α-tri-calcium phosphate. It was observed that the relative percentage of HAp reaches to its maximum amount in low levels of electrolyte concentration in small growth times but in high levels of electrolyte concentration in medium growth times. According to the observations of SEM and AFM, the layers with porous microstructures and rough surfaces were obtained whose pores sizes increased with time. Maximum amount of roughness was associated with the layers grown in higher concentrated electrolytes and medium process time, the layers presenting the best physical and chemical properties in order to be employed as bio-coatings. Based on XRD pattern, the average crystalline size of HAp was determined as

The SiO2-B2O3-CaO-K2O-Na2O-CaF2 system was considered to synthesize fluorcanasite dental glass-ceramic glaze for the first time. For this purpose, 3, 6 (wt.%) P2O5 and 0.5, 1 (wt.%) Li2O were added as additives for crystallization of nano-size fluroapatite and in order to lower the firing temperature respectively. The compositions were melted at 1450 °C for 2h in an electrical furnace then the resulting melt was quenched in water to obtain frit glass. After milling and drying the resulting frits were shaped by single–axis pressing in the form of tablets (diameter 10 mm and height 5 mm). There are four different temperatures for firing. The final phases in the optimum temperature were detected by XRD (X-ray diffraction). Chemical resistant of the samples was calculated after firing according to weight loss. Morphology of crystals by SEM and their elements analysis by EDX were studied, to add 0.5 (wt.%) Li2O and 5 (wt.%) P2O5 increase chemical resistance and reduce the glaze firing temperature to 930 °C. According to Standard Dental (ISO 6872) this glaze can be used as opaque shade on substrate of dental impact.

In the recent years, application of alumina-mullite composites in refractory industry has gained remarkable attention due to their high strength and life duration. In the present work, preparation of alumina-mullite composite was studied in optimal temperature and time condition using alumina nanopowder. Addition of alumina nanopowder in comparison with its micrometer sized powder in alumina-mullite composites increased mechanical strength and thermal shock resistant. Also, addition of micrometer and nanometer-sized alumina powder to alumina-mullite composites increased and decreased the thermal expansion coefficient, respectively. SEM and EDS analyses showed that the addition of alumina nanopowder increased the amount of mullite phase which improved the strength and thermal shock resistant. Also, addition of micrometer-sized alumina in alumina-mullite composite increased porosity and water absorption and decreased the density. The addition of alumina nanopowder decreased the porosity while water absorption increased the density.

In this study, Fe-Co and Fe-Co-Cr alloys produced by mechanical alloying method. This alloying percentage (Fe-35%Co alloy) is used because it has highest saturation magnetization among all alloys. Added chromium is by 10% (atomic percent). For this purpose, mixture of iron, cobalt and chromium powders were milled in planetary ball mill with speed of 300 and 400 rpm in 0.75, 1.75, 3, 10 and 20 h (for speed of 400 rpm) and 1, 15, 32, 60 and 90 h (for speed of 300 rpm). Different processes control agent is used in each speed. Effects of speed and PCA on powders cool welding to cup have been studied. Produced powders have been investigated by X-ray diffraction (XRD) method and scanning electron microscope (SEM) at different times of alloying. Crystalline structure crumbles more and more with increase milling time and is reached in nanoscale.

In the present study, non-uniform electric fields were applied as a simple cost-effective technique to manipulate ceramic nanoparticles for the fabrication of gas sensors. For this purpose, electrophoretic deposition of ZnO nanoparticles was performed on co-planar gold electrodes at 35 V for 15 min to obtain a crack free layer. Scanning electron (SE) and optical microscopy (OM) images showed that at 1 Hz, the obtained layer would be cracked. As the frequency was increased to 100 Hz and 1 kHz, particles presence within the electrode gap was reduced due to a change in deposition mechanism. At 10 kHz, considering the dominance of dielectrophoresis force exerted on the dipole moment of suspended particles, they were aligned along the electric field lines bridging the inter-electrode gap by forming chains which hindered crack formation. The optimized PCF conditions were then employed to fabricate a CO gas sensor which showed a clear and stable response to the target gas at 400, 450 and 500 °C.

In this research, calcium titanate nanoparticles synthesized via MASHS with spherical morphology and the lowest agglomeration. Phase development, morphology and particle size of calcium titanate were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and zetasizer analysis, respectively. X-ray diffraction analysis results confirm the formation of calcium titanate phase with high crystallinity after heat treatment. Also the uniform dispersion and spherical powder morphology, is well visible in SEM images. The results showed that after 70 h milling materials with ball to powder weight ratio of 70 to 1 and heat treatment for 1 h at a temperature 500 °C, to reduce agglomeration, defects formed during the milling process, improved morphology and reduce lattice strain, calcium titanate nanoparticles with an average grain size 35 nm and strain rate of 0.002 percent will be synthesized.

In this study, Fe-Co-Ni nanostructured alloy was synthesized by mechanical alloying route at different milling times. Morphology and microstructure of samples were investigated by scanning electron microscope and X-ray diffraction, respectively. Magnetic properties were measured by vibrating sample magnetometer. Fe45Co45Ni10 alloy with average grain size of 15 nm, was prepared after milling for 10 h and with further milling grain size and micostrain decreased. The powders exhibited minimum amount of lattice parameter (~ 0.28512 nm) after 20 h owing to triple defect disorder formation. Subsequent increase in lattice parameter (20 to 35 h) was due to grain size refinement. Coercivity decreased from 67 to 32 Oe after 2 h of milling as a result of effect of the very fine crystallite size (random anisotropy model), and then it increased gradually due to introduction of Ni and Co into the Fe lattice. Magnetic saturation increased from 85 to 185 Am2/kg as a result of alloying completion.

In this study, hydroxyapatite (HA) nanocomposite powder with 0, 4 and 8 wt.% silver were synthesized via sol-gel method. Phase formation, thermal stability, microstructure and particle size distribution were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), dynamic light scattering (DLS) and EDS mapping. Results showed presence of silver as a reinforcement phase caused a decrease in thermal stability of HA phase and decomposition of HA to β-TCP phase was increased. The microstructure characterization revealed that silver particles until 4 wt.% uniformly distributed in HA matrix and the particles were in nano-sized.